Give her a beautiful custom-made necklace with her name on Halloween. This is a very creative gift. You don't have to give her a gift that fits the theme of Halloween. Who knows, your bestie may not like those scary things, and won't attend parties. You will be embarrassed at that time. It's better to give her a creative gift. She can wear it at ordinary times, and it's harmless. Besides, the name necklace is a very special gift.
Sixteen is not yet an adult, so don't give her gifts that are beyond her age, such as brand-name bags. If she pays attention to brand names at such a young age, it's not good. Just give her a fashionable bag, no brand name is needed. You are besties, so you must know her habits. For example, she likes to play games, or likes to play chess, and some prefer literature. Give her gifts based on her hobbies. She has the habit of getting up and running every day. Give her a beautiful waterproof sports watch and comfortable sportswear. They are all good. As long as you have a heart, she will be happy with any gift.